Five major foodborne outbreaks of yersiniosis have occurred in the United States within the last decade and the disease is endemic in many other countries of the world. Yersinia enterocolitica is of particular concern to the food industry because it is a psychrotroph, and, therefore, growth can not be controlled by refrigeration. Laboratory methodology presently available for detecting Y. enterocolitica is time-consuming. Two unique antigenic structures on pathogenic strains of Y. enterocolitica present the basis for developing an immunoassay for rapid detection of Y. enterocolitica: (i) unique outer membrane proteins synthesized at 37 C by strains that carry a virulence plasmid, and (ii) flagella. Specific antibody will be incorporated into two experimental immunoassays: (i) a disperse dye system, and (ii) an avidin-biotin enzyme system. An immunoassay can be assembled as a marketable test kit for rapid detection of Y. enterocolitica in foods. A long-term objective is the development of antigen and antibody detection systems for rapid identification of Y. enterocolitica and measuring serological responses in clinical microbiology.